PROJECT 1 Viral infections targeting glia and neurons commonly cause encephalitis and have high mortality. Long term neurological dysfunction potentially resulting from altered cell function in persistently infected cells or immune pathology are common. Type I interferons (IFNa/(3) provide the first line of host defense against viral spread to and within the CNS. However, little is known about the ability of resident CNS cells to mount innate responses during acute or persistent CNS infections. This proposal addresses how distinct IFNa/p responses in microglia, astrocytes and oligodendrocytes contribute to pathogenesis following infection with a non lethal, demyelinating neurotropic coronavirus. Despite the concerted efforts of IFNa/p and adaptive immune cells to prevent mortality, virus is incompletely cleared, resulting in viral RNA persistence in the CNS. The overall hypothesis tested is that narrowly focused innate signals by oligodendrocytes constitute a protective mechanism for their survival and function in maintaining myelin, at the cost of persistent infection. Induction of IFNa/p by microglia and/or astrocytes is critical to induce an antiviral state in an autocrine and paracrine fashion. Aim # 1 will establish whether CNS cell types with highly specialized function, e.g. oligodendrocytes, rely on other cell types to signal the presence of invading pathogens. A dependence of IFNa/p signaling by individual cell types for protection will be confirmed by conditional abrogation of IFNa/p signaling in oligodendrocytes, astrocytes and microglia. Aim #2 will analyze mechanisms of RNAseL mediated protection against virus induced demyelination. It is based on novel findings of significantly enhanced demyelination and mortality of virus infected RNAseL deficient mice, despite effective viral control. Aim #3 will reveal whether persistently infected oligodendrocytes are immunologically silent, or trigger sufficient innate responses to directly or indirectly sustain local inflammation and demyelination. The overall approaches rely on a combination of RNA expression analysis in glial populations isolated directly from the infected CNS, immunohistochemical analysis, and chimeric mice to distinguish between innate affects on resident versus infiltrating cells. By defining mechanisms of innate immune regulation within the CNS during both acute and persistent infection, these studies will benefit our understanding and manipulation of factors critical for both anti viral function and amelioration of pathology manifested by demvelination.